Rechargeable batteries are used for many purposes. One application of increasing importance is as a power source for automobiles and other vehicles. In many cases, batteries are used to cold crank internal combustion engines. They are also used to power a vehicle's cabin accessories such as lights, audio systems, navigation systems, seat warmers, etc. With the market establishment of hybrid and all electric automobiles, rechargeable batteries are increasingly used to power the propulsion of the automobile. Another common application for rechargeable batteries is in uninterruptible power supplies (UPS), which provide emergency power to a load in the event that a primary source of power goes down. UPSs are commonly used to ensure near instantaneous protection from loss due to power outages for data centers, telecommunications equipment and other critical electrical equipment.
Battery Management Units (BMUs) are sometimes employed to control the charging and to maintain a suitable state of charge in battery packs for applications such as automotive and UPS applications. An alternator may be used to deliver electronic charge to the batteries.